First, it's not Facebook, and I'm not the only Facebook hater.
Second, it's a second chance at your online persona. Ezra Klein explains:
At this point, most of us have Facebook friends dating back to three or four distinct eras in the evolution of social networking. That’s made it very hard to know how to use your Facebook account. I, for one, have mostly stopped using mine. I don’t want to annoy my acquaintances with the content I want to send my closer friends, nor do I want to annoy my closer friends with the content suitable for my acquaintances.
Facebook has tools for managing all this, but they’re hard and awkward to use. Will people notice that they suddenly can’t see your photographs anymore? If you defriend them, will they take it personally? Do I have time to defriend 400 people? What I need, and what I think a lot of other people need, is an opportunity to start over. But you can’t start over on Facebook. That’s awkward. And no other social network has sufficient density to make joining worthwhile.
That’s where I could imagine Google+ coming in. It’s not that any of its features are so revolutionary. It’s not that it’s better at doing social networking than Facebook. It’s that it’s an opportunity to start over, to build your social network with years of Facebook experience in mind, rather than having to face the accretion of mistakes and miscalculations you made over almost a decade of trial-and-error with a new technology. It’s not Facebook’s fault that “what it means” to have a Facebook account has changed four or five times over the last few years, even as most of us have only had one profile over that period. But it is an opportunity for Google.But mostly it's because I hate Facebook.